If a block takes indirect sweep damage (sword), the resulting damage to the block immediately behind the mobs does not timeout/auto repair. The cumulative damage can be demonstrated behind mobs in a 1x1 xp grinder, where the block behind the mobs takes slowly accumulating damage over time until it breaks.
Tapping the block directly one time causes the damage timeout to activate and the block to removed the accumulated damage.
Specifically, tested on StoneBrick block.
please provide screenshots of your issue and setup